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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

A vacuum (10(exp -9) Torr) friction apparatus for determining friction and endurance life of MoSx films

The first part of this paper describes an ultrahigh vacuum friction apparatus (tribometer). The tribometer can be used in a ball-on-disk configuration and is specifically designed to measure the friction and endurance life of solid lubricating films such as MoS(x) in vacuum at a pressure of 10 exp -7 Pa. The sliding mode is typically unidirectional at a constant rotating speed. The second part of this paper presents some representative friction and endurance life data for magnetron sputtered MoS(x) films (110 nm thick) deposited on sputter-cleaned 440 C stainless-steel disk substrates, which were slid against a 6-mm-diameter 440 C stainless-steel bearing ball. All experiments were conducted with loads of 0.49 to 3.6 N (average Hertzian contact pressure, 0.33 to 0.69 GPa), at a constant rotating speed of 120 rpm (sliding velocity ranging from 31 to 107 mm/s due to the range of wear track radii involved in the experiments), in a vacuum of 7 x 10 exp -7 Pa and at room temperature. The results indicate that there are similarities in friction behavior of MoS(x) films overs their life cycles regardless of load applied. The coefficient of friction (mu) decreases as load W increases according to mu = kW exp -1/3. The endurance life E of MoS(x) films decreases as the load W increases according to E = KW exp -1.4 for the load range. The load- (or contract-pressure-) dependent endurance life allows us to reduce the time for wear experiments and to accelerate endurance life testing of MoS(x) films. For the magnetron-sputtered MoS(x) films deposited on 440 C stainless-steel disks: the specific wear rate normalized to the load and the number of revolutions was 3 x 10 exp -8 mm exp 3/N-revolution; the specific wear rate normalized to the load and the total sliding distance was 8 x 10 exp -7 mm exp 3/N-m; and the nondimensional wear coefficient of was approximately 5 x 10 exp -6. The values are almost independent of load in the range 0.49 to 3.6 N (average Hertzian contact pressures of 0.33 to 0.69 GPa).

Miyoshi, Kazuhisa↗
NASA NTRS2009

The UAH/NSSTC Advanced Radar for Meteorological and Operational Research (ARMOR)

The past four years have seen a marked enhancement in meteorological-radar infrastructure and radar-research capability at the University of Alabama-Huntsville (UAH) and National Space Science and Technology Center (NSSTC; a collaborative center supported by UAH, NASA-MSFC and USRA). This enhancement is due in part to the development of the ARMOR C-band dual-polarimetric radar facility (amongst other mobile radar facilities also discussed in this conference). The ARMOR radar, located at Huntsville International Airport, originated as a unique collaboration between university, government and broadcast meteorologists (the very first of its kind relative to concurrent operational, research and broadcast applications of dual-polarimetry). Contributions from each of these entities resulted in the upgrade of a surplus National Weather Service WSR-74C radar to a research-grade C-band polarimetric radar. The initial upgrade of the radar took place in late 2004 with WHNT-TV purchase and installation of a SIGMET (now Vaisala) Antenna Mounted Receiver (AMR), RVP8/RCP8 radar processor/antenna controller, new radome, and a new dual-polarimetric antenna feed. The AMR enabled simultaneous transmit and receive (STSR) capability and hence collection of dual-polarimetric moments. During the initial part of the AMR upgrade the original WSR74C antenna reflector and 250 kW magnetron-transmitter were used. In early 2005, a new 350 kW magnetron transmitter was purchased from Baron Services and installed. In October of 2006 a new high performance parabolic antenna and dual-pol feed (Seavey) were installed together with a new Orbit pedestal. ARMOR Radar control and data delivery are facilitated through the use of T-1 lines that run from the airport to both NSSTC and WHNT-TV in Huntsville. Under current operating protocols radar scanning and product development are completed at NSSTC, though meteorologists at WHNT-TV can also control the radar if desired. In its default scanning configuration the radar is operated 24/7 in an STSR polarimetric rain scan mode alternating with a surveillance scan on a 5-minute cycle; scans separated by 2.5 minutes. Every 2.5 minutes the raw data arrive at NSSTC where they are corrected in real time for attenuation and differential attenuation (using a constrained ZDR/Z-PHI approach) and new products are generated (e.g., rain maps, hydrometeor identification etc.). The raw and derived products are archived at NSSTC and also redistributed locally in real time over the network within NSSTC to the National Weather Service Forecast Office in Huntsville (collocated with NSSTC) for operational use. During periods of interesting weather the radar is often operated in full, sector, or RHI volume modes from NSSTC and coincident with UAH mobile radar or NWS NEXRAD radar platforms as needed.

Petersen, Walter A.↗
NASA NTRS2019

Molten Target Sputtering: Non-Conventional Method for High Mobility Si0.15Ge0.85 Growth at 500°C

Since electrons travel over 100 times faster in Silicon-Germanium (SiGe) than in pure Si due to the low effective masses associated with Ge and SiGe-based devices continue to replace Si-based solid-state electronic devices. SiGe thin film on sapphire was successfully grown at 890°C, using a magnetron sputtering system within heteroepitaxial framework. However, SiGe growth at 890oC is a costly and difficult process to produce as a uniform wafer for semiconductor device manufacturing due to thermal soak times, and geometric thermal shadowing from the wafer holder. To leverage the semiconducting capabilities of SiGe, novel processing techniques for SiGe film growth with decreased thermal loading are required. This paper introduces the Molten Target Sputtering (MTS) method that produces high mobility SiGe on sapphire below 500°C. This non-conventional method has the advantage of high kinetic energy, high-energy latency, and high flux density of sputtered atoms by combining benefits of both magnetron sputtering and thermal evaporation. For the MTS method, a 1~2 mm (depth and width) ring-shaped groove was cut between the center magnet and surrounded by electromagnets creating a circular cavity between the copper plate and source target materials that melt the target material. The SiGe grown from the MTS shows continuous morphology and 99.7% single crystal Si0.15Ge0.85 films. The Hall electron mobilities of the Si0.15Ge0.85 are 456 sq. cmV(exp -1)s(exp -1) and 123.9 sq. cmV(exp -1)s(exp -1) at 5.59 x 10(exp 18) cubic cm and 3.5 x 10(exp 20) cubic cm carrier concentration at 22.38°C, respectively. This is approximately 5.5 times higher than that of Si and similar to the Ge value at equivalent carrier concentrations and temperatures.

High mobility SiGe↗
DOE OSTI2017

Soft Magnetic Properties of Hf{sub x}Co{sub 100−x} Thin Films

Hf{sub x}Co{sub 100−x} thin films (in the atomic weight range of x = 30–36) were growth on Si (100) substrates by direct current (DC) magnetron sputtering method. Thin films produced with atomic compositions in this context depicted the amorphous structure. The films revealed soft magnetic properties and thus exhibited very low hysteresis along the hard-axis direction. Magnetic measurements indicated that Hf{sub 35}Co{sub 65} thin film has the maximum saturation magnetization (1491 emu cm{sup −3}) at 300 K. Additionally, magnetization measurements show an increase in saturation magnetization value from 981 to 1491 emu cm{sup −3} when the value of x varies between 30 and 35. The influence of varying sputtering pressure and film composition on soft magnetic properties are investigated and discussed in the present paper.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Nano-size Analysis through Magnetization Data for Developed Mn{sub 0.5}Zn{sub 0.5}X{sub 0.2}Fe{sub 1.8}O{sub 4} (X = Fe, Gd, La, Sm)

Mn{sub 0.5}Zn{sub 0.5}X{sub 0.2}Fe{sub 1.8}O{sub 4} (X = Fe, Gd, La, Sm) nano-ferrite were synthesized by chemical co-precipitation method. Magnetic measurements for the synthesized Mn{sub 0.5}Zn{sub 0.5}X{sub 0.2}Fe{sub 1.8}O{sub 4} (X = Fe, Gd, La, Sm) nano-particles were recorded at temperatures 10 and 300 K. Magnetic moment per unit formula in terms of Bohr magnetron (μ{sub B}) was calculated from magnetization data of hysteresis loops. Particle size was calculated from the magnetization data for all compositions of Mn{sub 0.5}Zn{sub 0.5}X{sub 0.2}Fe{sub 1.8}O{sub 4} (X = Fe, Gd, La, Sm) ferrite particles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Study of Electrical Transport and Magnetic Properties of Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Nd{sub 0.8}Na{sub 0.2}MnO{sub 3} Bilayer Thin Films

Bilayer films of Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Nd{sub 0.8}Na{sub 0.2} MnO{sub 3} were grown on 001-orientated LaAlO{sub 3} substrate by using RF magnetron sputtering. The thickness of the Nd{sub 0.8}Na{sub 0.2}MnO{sub 3} (NNMO) film was kept fixed at 120 nm while that of the Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3} (NSMO) film was varied from 12 to 100 nm. X-ray diffraction patterns confirm the growth of films along the (001) direction, and the out-of-plane lattice constant of the NSMO film decreases with an increase in film thickness. The bilayer films are found to undergo out-of-plane tensile strain, and the lattice strain is found to decrease with an increase in film thickness. The ferromagnetic transition temperature is found to increase with an increase in the NSMO film thickness. M–H loops recorded at 50 K show a systematic increase in saturation magnetisation with an increase in film thickness. Metal–insulator transition has been observed for the film thickness of 30 nm and above, and the transition temperature is found to increase with an increase in film thickness. The electrical resistivity data in the metallic region were explained based on electron–electron and electron–magnon scattering mechanism by including a weak localisation effect at low temperature. The electrical resistivity data in the insulating region follow the Mott-variable range hopping model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of Thickness on Structural and Magnetic Properties of Co-rich Bi{sub 10}Co{sub 16}O{sub 38} Sillenite Thin Films

The effect of thickness on structural and magnetic properties of Co-rich Bi{sub 10}Co{sub 16}O{sub 38} (BCO) sillenite thin films is investigated systematically. BCO thin films are deposited using a simultaneous evaporation of Bi{sub 2}O{sub 3}, Co targets with RF-DC magnetron sputtering along with post-annealing procedure. The magnetic studies reveal an ordered magnetic nature below film thicknesses of 100 nm. Further, the temperature-dependent and field-dependent magnetic data is evaluated to comprehend the microstructure impact on to the magnetic nature of Co-rich sillenite thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ti Capping Layer Effects in Microstructure and Magnetic Properties of Sputter-Deposited FePt Thin Film

Ti/FePt/Fe nano-thin films were fabricated by a DC facing-target magnetron sputtering method onto glass substrates at room temperature and were subsequently annealed in situ in vacuum. The impacts of the Ti capping layer on microstructural and magnetic properties of the FePt films were investigated in detail. X-ray diffraction (XRD) patterns demonstrate that the film is deposited onto glass substrates and the addition of a Ti layer forms ternary TiFePt, and binary PtTi and FeTi alloys. The results reveal refined granularity, decreased roughness, and enhanced coercivity and degree of squareness after the introduction of a Ti capping layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Preferred Orientation Enhancement in FeCo/SiO{sub 2} Nanocomposite Films Induced by Cu Underlayer

We prepared FeCo/SiO{sub 2} thin films through depositng initial materials on various thickness Cu seed layers by sol-gel spin-coating and magnetron-sputtering methods. As-prepared composite films were reduced in hydrogen to induce texture growth. Structure, magnetic property, and surface topography of the films were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and atomic force microscopy (AFM). These experimental data indicate that the ratio values of I{sub (200)}/I{sub (110)} of the thin films are all larger than 1 for all the samples, indicating that FCC-copper is in favor of promoting (200) FeCo texture, but more thickness will reduce this advantage. Cu underlayers can also promote the out-of-plane magnetic anisotropy of the films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Thickness-Dependent Thermal Oxidation of Ni into NiO Thin Films

We report thickness-dependent thermal oxidation in Ni (t = 10–300 nm) thin films exposed to air annealing and the resulting vibrational, magnetic and electrical properties of Ni films deposited directly on thermally oxidized Si substrate using magnetron sputtering technique at ambient temperature. As-deposited Ni films exhibit face-centred cubic structure with fine crystals and large lattice constant (a{sub Ni}) at lower t (< 50 nm). With increasing t, a{sub Ni} decreases and approaches to bulk value. With increasing T{sub A}, a{sub Ni} not only decreases to bulk Ni due to improved crystallization but also reduces below bulk Ni for t > 50 due to formation of NiO. The relative fraction of Ni and NiO in annealed films up to 400 {sup ∘}C strongly depends on t. Annealing Ni films at 500 {sup ∘}C results into complete oxidation of Ni into granular-type NiO. X-ray reflectivity studies reveal that oxidation process occurs from surface of the films converting Ni into NiO possibly through layer by layer process, which is subtle to t. Raman spectra show that intensity ratio between one-phonon longitudinal optical (LO) and two-phonon LO bands decreases and intensity of two-magnon band increases with increasing t for films annealed at particular T{sub A}. This confirms the growth of NiO not only with increasing T{sub A}, but also with t. As-deposited films exhibit ferromagnetism at room temperature. The presence of Ni and NiO in annealed films implies coexistence of ferromagnetic and antiferromagnetic interactions, leading to tunable exchange bias (H{sub E}), whose magnitude strongly depends on the ratio between Ni and NiO. Electrical resistance (R) of the as-deposited Ni films decreases with increasing t and follows the Namba’s model. Upon annealing, R increases largely due to oxidation of Ni. The observed results are explained on the basis of thickness dependent thermal oxidation process with increasing T{sub A}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Substrate Temperature on Structural, Morphological, Magnetic, and Electrical Properties of Fe{sub 2}CoSi Heusler Alloy Thin Films for Spin-Based Device Applications

Fe{sub 2}CoSi based Heusler alloy thin films are deposited on single crystal Si (111) substrate at different substrate temperatures varying from room temperature to 600 °C using ultrahigh vacuum DC magnetron sputtering. Structural analysis of the prepared thin films is carried out using GI-XRD measurement and it conform ordered L2{sub 1} crystal structure of the films deposited at 450 °C and above. The atomic force microscopic (AFM) images of Fe{sub 2}CoSi thin films exhibiting 3D-like growth on Si (111) substrate at varying temperatures. The magnetic property of the thin films is studied using vibrating sample magnetometer (VSM). At 450 °C of substrate temperature, the prepared thin film exhibits high saturation magnetization (M{sub s} = 948 emu/cc) and low coercivity (H{sub c} = 8 Oe). The self-energy magnetization of the film and its own field is very high, when the temperature of the substrate was maintained at 450 °C and switching field ratio for this film was obtained as ~ 0.9 due to its high crystallinity and atomic ordering. The electrical property of Fe{sub 2}CoSi thin film is investigated using four-probe technique and a positive magnetoresistive behavior was observed for thin film deposited at a substrate temperature of 450 °C which indicates the possible half-metallic nature at room temperature. The enhanced magnetic and electrical properties obtained for the thin film prepared at 450 °C substrate temperature is highly suitable for spin based device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

FMR and Magnetic Studies of RF-Sputtered Mn-Zn Ferrite Thin Films

The Manganese–Zinc ferrite (MZF) thin films were deposited on quartz substrates by radio frequency (RF) magnetron sputtering at 10 mTorr of argon gas pressure. The FMR and magnetization measurement were carried out to understand magnetic properties of the as-deposited and annealed MZF films. The resonance field (H{sub r}) of the FMR spectra shifts towards higher magnetic field when angle between applied field and thin film plane is changed from 0 to 90° indicating the existence of uniaxial anisotropy in the film. Whereas, H{sub r} shifts towards lower magnetic field with decrease in temperature of the film. This is due to ferrimagnetic ordering in the films at low temperatures. The magnetization versus field (M-H) plots reveal the soft ferrimagnetic behavior of the films. The post-deposition annealing of the film leads to increase in crystallite size with more uniform film surface and dense columnar growth compared to the as-deposited film. The increase in magnetization and decreases in H{sub r}-values compared to that of as-deposited film are observed for annealed film. The optical band gap of the film is also found to increase with annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Anomalous Hall Effect in Epitaxial Ni–Mn–Ga Thin Films Grown on MgO(001) Substrate during the Martensitic Transformation

Epitaxial Ni–Mn–Ga thin films had been grown on MgO (001) by DC magnetron sputtering. And the anomalous Hall effect (AHE), microstructures, magnetism, and magnetoresistance (MR) were investigated. The AHE was measured in the film of Ni{sub 47.8}Mn{sub 30.8}Ga{sub 21.4} during the martensitic transformation. Meanwhile, the mechanism of the AHE was explained which indicates that the hall resistivity measured in our sample is primarily determined by AHE. The microstructures of the austenite phase and 7M martensite plates at room temperature had been observed on the film of Ni{sub 46.7}Mn{sub 31.7}Ga{sub 21.6} and Ni{sub 47.8}Mn{sub 30.8}Ga{sub 21.4}, respectively. Magnetic measurements reveal that all films possessed the martensitic transformation during the heating and cooling processes. In addition, the MR showed a negative value during the martensitic transformation which is mainly due to the reduction of spin-dependent scattering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Relation between carriers hopping rate and structural constants in amorphous carbon nickel films with different nickel nanoparticles distributions

In this paper, the films were prepared by radio frequency magnetron co-sputtering technique. The effect of different mosaic targets made of nickel strips and graphite pure on the dielectric relaxation time, the carriers hopping rate, the fractal dimensions and the optical loss of films were studied. The values of the optical band gap of films using the cross-point between the tangent of the plot of lower and higher values of the photon energy were calculated. The films deposited at 4.64% have maximum hopping rate of about 8.6 × 10{sup 12} S{sup −1}. It can be seen that the films deposited at 3.92% have minimum value of fractal dimension of 2.27. With increasing Ni content of films a nonmetal–metal transition is observed which it is explainable by the power law of percolation theory. Critical metal content and the critical exponent of films were 87.25% and 1, respectively. With increasing Ni content, the carriers effective mass of films decreased and average lattice separation values of films increased. Films deposited at 3.92% have minimum value of Debye frequency ν{sub D} of about 1.09 × 10{sup 12} Hz. The value of energy loss by free charge carriers when traversing the bulk and surface of films at 3.92% has maximum value and it has an increasing function behavior with energy.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Liquid-Phase Surface Alloying of Copper with Stainless Steel Using Low-Energy, High-Current Electron Beam

The paper deals with the formation of the stainless steel-copper surface alloy which occurs during the single vacuum cycle. Deposition of the stainless steel film onto a copper substrate is performed via successive magnetron sputtering followed by its liquid-phase mixing with copper using the low-energy, high-current electron beam of microsecond length. Numerical calculations are used to identify the optimum irradiation modes for the surface alloying. It is found that the optimum irradiation modes provide the homogeneous surface alloying, and the copper concentration in the obtained layer increases with the increase in energy density of the low-energy, high-current electron beam. The formation of the stainless steel-copper surface alloy increases the wear resistance of copper specimens by 7.5 times as compared to the original specimens. In addition, it is ascertained that the wear resistance of the surface alloy exceeds that of the common film coating (1 μm) more than 5 times.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Characteristics of Hydrogen Sensors Based on Thin Tin Dioxide Films Modified with Platinum, Palladium, Silver, and Yttrium

The dependence of the characteristics of hydrogen sensors based on thin Pt/Pd/SnO{sub 2}:Sb, Ag, Y and Ag/SnO{sub 2}:Sb, Ag, Y films obtained by the method of magnetron sputtering at a direct current on the humidity level of the gas mixture during operation in thermal cyclic mode is investigated. The analysis of the experimental data was carried out using the expressions obtained on the basis of the dissociative adsorption model of hydrogen and water molecules on the SnO{sub 2} surface, taking into account the presence of three types of adsorbed particles: O{sup –}, OH, OН{sup –}. The use of complex modifiers Pt/Pd, Ag on the surface and Ag + Y in the bulk of tin dioxide films allows to reduce the influence of humidity on the characteristics of sensors. The role of these modifying additives in the process of dissociative adsorption of hydrogen molecules on the surface of SnO{sub 2} films in humid environment is established.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Physical Properties of Solid Solutions In{sub x}Al{sub 1–x}N

The phase diagrams and the results of studies of the GaN, AlN and InN ternary solid solutions grown using the magnetron sputtering, molecular beam epitaxy, and metalorganic vapour-phase epitaxy technologies and intended for the production of ultrahigh-frequency InAlN/GaN HEMT transistors are analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Sputtering Current on the Comprehensive Properties of (Ti,Al)N Coating and High-Speed Steel Substrate

To improve the practical property of (Ti,Al)N coating on a high-speed steel (HSS) substrate, a series of sputtering currents were used to obtain several (Ti,Al)N coatings using a magnetron sputtering equipment. The phase structure, morphology, and components of (Ti,Al)N coatings were characterized by x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy, respectively. The performance of (Ti,Al)N coatings, adhesion, hardness, and wear resistance was tested using a scratch tester, micro/nanohardness tester, and tribometer, respectively. Based on the structure–property relationships of (Ti,Al)N coatings, the results show that both the Al content and deposition temperature of (Ti,Al)N coatings increased with sputtering current. A high Al content helped to improve the performance of (Ti,Al)N coatings. However, the HSS substrate was softened during the high sputtering current treatment. Therefore, the optimum sputtering current was determined as 2.5 A that effectively increased the hardness and wear resistance of (Ti,Al)N coating.

36 MATERIALS SCIENCE↗